Fuse holders for fuse cutouts and the like are known in the art. For example, in electrical distribution systems, a fuse cutout is a combination of a fuse deployed in a fuse holder and a switch found primarily in overhead feeder lines to protect distribution systems and transformers from current surges and overloads. If equipped with appropriate mechanisms, cutouts can act as sectionalizers, used on each distribution line downstream from autoreclosing circuit breakers. Autoreclosers sense and briefly interrupt fault currents, and then automatically reclose to restore service. Meanwhile, downstream sectionalizers automatically count current interruptions by the recloser. When a sectionalizer detects a preset number of interruptions of fault current (typically 3 or 4) the sectionalizer opens (while unenergized) and remains open, and the recloser restores supply to the other non-fault sections.
A fuse cutout consists of three major components. The first component is the cutout insulator body, a generally open “C”-shaped frame that supports a fuse holder and a ribbed porcelain or polymer insulator that electrically isolates the conductive portions of the assembly from the support to which the insulator is fastened. The second component is the fuse element, or “fuse link”, which is the replaceable portion of the cutout assembly that operates when the electrical current is great enough. The third component is the fuse holder, also called the “fuse tube”, which is an insulating tube which contains the replaceable fuse element. When the fuse element operates (“blows”), the fuse holder breaks the circuit, then drops out of the upper contact, and hangs from a hinge on its lower end. The hanging fuse holder provides a visible indication that the fuse has operated and assurance that the circuit is open.
An overcurrent caused by a fault in the transformer or customer circuit will cause the fuse to melt, disconnecting the transformer or faulted circuit from the line. To facilitate disconnection, cutouts are typically mounted about 20 degrees off vertical so that the center of gravity of the fuse holder is displaced and the fuse holder will rotate and fall open under its own weight when the fuse blows. Mechanical tension on the fuse link normally holds an ejector spring in a biased position. When the fuse blows, the released spring pulls the stub of the fuse link out of the fuse holder tube during the fault clearing process. The electric arc is quenched within the fuse holder, limiting duration of the fault event. The cutout can also be opened manually by utility linemen standing on the ground and using a long insulating stick called a “hot stick”.
In operation, after the fuse link has blown and the fuse holder drops, a lineman replaces the fuse link and re-deploys the fuse tube in its operating condition. The fuse holder is also equipped with a pull ring that can be engaged by a hook at the end of a fiberglass hot stick operated by a lineworker standing on the ground or from a bucket truck, to manually open the switch.
As will be appreciated by one of ordinary skill in the art, up until the mid-1970s, each manufacturer used their own dimensional standards for cutout designs. The plethora of designs resulted in the inability to use replacement fuse holders from one manufacturer to service or repair the cutouts of another manufacturer. By the late 1980s, the industry moved to a standard design that resulted in the interchangeability of fuse holders between the manufacturers. In other words, the interchangeable design allows for the interchangeable use of cutout bodies, fuse holders, and fuses manufactured by different vendors.
One drawback with the adoption of interchangeable designs is the stagnation of the state of the art. In an effort to maintain the interchangeability of the parts, little has been done to improve upon existing designs. Such stagnation has led to the inevitable problems of acquiescence in the configuration and expense of the parts and materials, and in particular that of the fuse holder; as well as acquiescence in component failure rates such as those known in the art occurring from heating, melting, and welding that are currently deemed unavoidable and a fact of life when it comes to fuse tubes.
The foregoing underscores some of the problems associated with conventional fuse holders. Furthermore, the foregoing highlights the long-felt, yet unresolved need in the art for a fuse holder that lessons the phenomena of heating, melting, and welding that are associated with prior art fuse holder. Moreover, the foregoing highlights the long-felt, yet unresolved need in the art for a fuse holder that has an extended service life at a reasonable cost.